1. Technical Field
This invention relates generally to systems and methods for the delivery of laser light for therapeutic purposes, and, more specifically, to laser light delivery systems for the treatment of buried tumors.
2. Background
Laser/tissue interactions and therapeutic applications of laser light are two rapidly growing areas of research. As is well known to those skilled in the art, high intensity laser beams have the potential to destroy bodily tissue, a property that can be turned to usefull purposes in the field of tumor treatment, where the term "tumor" will be used hereinafter to describe any cellular mass that serves no physiological function including cancers, neoplasms, neoplastic masses, etc. The growth of a tumorous mass can be retarded or even stopped through the application of thermal energy, and a laser provides a precise, concentrated, and highly controllable means of delivering that energy. Tumors on the surface of the body--and those that can be made visible through surgery or other means--are excellent candidates for such treatment and often respond favorably to the direct application of laser light. However, tumors that are buried deep within healthy tissue pose a special problem for laser methods. In more particular, since lasers are ultimately just coherent light sources, any attempt to "illuminate" a buried tumor with laser light must necessarily also illuminate the tissue that lies between the laser source at the surface and the tumor. Thus, the heat from a laser that is directed at a buried target has the potential to destroy, not only the tumor, but also to the tissue that encloses it.
Basic physics provides an explanation of why this should be so. Biological tissues are turbid media and light that passes therethrough is continually absorbed by the conducting tissue during its passage. Additionally, bodily tissue is a strong light scatterer and additional energy is lost from the beam during its transmission due to this effect. The absorbed and scattered radiant energy is converted into thermal energy (heat), which energy has the potential to damage the tissue within and along a laser beam's path. These two effects can combine to substantially reduce the potential effectiveness of laser treatment of buried tissues because each unit of radiant energy that is lost during the beam's transmission to the tumor represents one less unit of energy that can be applied to heat its ultimate target. Thus, one of the principal obstacles to the use of laser light to treat a buried tumor is that the tumor may potentially receive much less optical power than the surrounding subsurface healthy tissues.
Broadly speaking, there are three general approaches to overcoming the aforementioned obstacle, the ultimate goal being to maximize the power delivered to the target tumor while minimizing the risk of collateral damage to other tissues. First are dye-based treatments which aim to increase the light absorption coefficient of the tumor by infusing it with one or more special dyes. This makes possible the use of a lower power laser light source, as the dye-infused tumor will tend to heat more rapidly than the surrounding tissue. Another approach involves manipulation of the wavelength of the laser light and the selection of a wavelength to which the tumor is more responsive than is the surrounding normal tissue. Finally, a third broad approach involves selection of a light delivery scheme which maximizes the power absorption by the target tumor and minimizes the exposure of the surrounding tissue to thermal stress. The present invention is directed to this last approach.
Thus, what is needed is a laser delivery system that can efficiently convey a maximum amount of optical power to a buried tumor while reducing the risk of collateral damage to the surrounding normal tissue. Additionally, it should also be designed so that the laser light is selectively applied to tumorous tissue rather than normal tissue. Finally, the lasers that comprise the system should be sized such that they maximize the power coupling efficiency and the power delivered to the buried tumor.
Accordingly, it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a laser light delivery system that would address and solve the above-described problems.
However, before proceeding to a description of the present invention it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.